Today's Gospel reminds us of two of the great
miracles God has built into nature. The mustard seed is quite tiny -- a little
bit smaller, even, than those poppy seeds that you often see on Kaiser rolls.
And yet, in spite of its very small size, it grows up literally to the size of a
tree. Likewise the leaven is just a little bit of yeast that is mixed with
dough, but which causes the entire loaf of bread to rise. Through God's design,
both of these two things -- the leaven and the mustard seed seem to have an
effect that is out of proportion to the thing itself.

But, of course, our Lord did not tell this story -- this
parable -- to teach a lesson in agriculture or baking. Like many of his
parables, the leaven and the mustard seed point to realities beyond the scope of
their humble little story. In this case our Lord did not explain His exact
meaning to the Apostles, but it is not hard to guess what He had in mind:

Very likely, the grain of mustard seed is like the faith
of a Christian who strongly believes in God. Faith is much like a seed that we
allow God to plant in our minds. We can't have it without receiving it from God,
any more than a mustard tree can grow without first having a mustard seed. And
even if we do have the faith, it must be nurtured and protected; for just like
the mustard seed, faith is relatively easy to uproot in its early stages; and
faith requires the right climate in which to grow, just as the mustard seed
needs the sun and the rain. But even though faith starts out like a small seed,
under the proper circumstances it can grow to be a great thing. We see those who
are strong in faith supported in life even in the face of many difficulties.
Often too, a really strong faith will even support other people, who come and
take refuge in it, much like the birds who rest on the branches of the mustard
bush.

The measure of leaven is like the good example of one who
practices his faith all of the time; whether anyone is looking or not; whether
times are good or bad. Good example is what Saint Paul was referring to in his
letter this morning to the Thessalonians. By imitating him, and particularly by
imitating our Lord, they became a "pattern to all the believers" in
their part of the world. "Macedonia and Achaia," by the way, are the
ancient names for the countries we knew after World War II as Yugoslavia,
Bulgaria, Albania, and Greece -- a rather significant area to influence for the
better by one's good example.

Whether it be at the level of the nation, or the
community, or the parish, or the family, this good example of the faith is
always the key to spreading the good news of Jesus Christ among those who have
not heard it; it is always the key to getting those who have heard it to act
upon it and make it part of their own lives. How can we expect our children or
our neighbors or the other countries of the world to behave as Christians if we
fail to do so ourselves? How can we expect others to pray or to keep the
commandments if we do not ourselves? Just as it is impossible for the tree to
sprout without the seed, and just as it is impossible for the loaf to become
leavened without the bit of yeast, it is impossible for us to communicate the
Catholic Faith to others if we do not have it ourselves.

And having the Faith without practicing it is like having
sterile seed or yeast. Organisms like yeast and seeds become sterile if they are
exposed to heat or radiation -- by sterile, I mean that they still look the
same, but they produce no offspring: no tree grows, and no loaf rises; even
though we start out with what looks like seed or what looks like yeast.

So how are we to practice the Faith? What can we do to
nurture and protect it? Well, to begin with, faith is a virtue of the intellect;
it is by faith that we come to know God as He has revealed Himself to the world.
But all of the knowledge in the world, even if it is about God, remains a
sterile thing in itself. Something more must compliment that knowledge if it is
to be of practical use. Not surprisingly, what is needed to make faith useful is
the companion virtue of charity. The two really work together: you cannot
love God if you do not know Him, you will not bother to know God very well if
you do not love Him.

Like all virtues, even natural virtues, faith and charity
must be practiced in order to be developed. But both of these virtues come from
God. If we are to develop them in ourselves we must do so in cooperation with
God; and by cooperation with God I mean things like prayer, and receiving the
Sacraments, and performing the spiritual and corporal works of mercy for those
around us -- and doing these things whether or not anyone is looking, in season
and out, whether times are good or bad.

How can our good example be like that of the
Thessalonians? How can we give such testimony? The best way I have ever heard it
expressed was by the French Cardinal Emmanuel Suhard: "To be a witness does
not consist in engaging in propaganda, nor even in stirring people up, but in
being a living mystery. It means to live in such a way that one's life would not
make sense if God did not exist."

And that, I think, is the meaning of this parable of
mustard seed and leaven. Great power is contained in the faith of the humble
believer -- indeed, it is the power of God. It must not be allowed to become
sterile; it must be "a living mystery." It grows to its full potential
in us only when we live life in a way that "would not make sense if God did
not exist."